Sensitised heat sensitive printing plate precursors

Abstract

A lithographic printing plate precursor comprises a grained and anodised aluminium substrate coated with a metallic layer, preferably a silver layer, on top of which is applied a layer comprising at least one sensitising material which adsorbs on to the metallic surface and thereby sensitises the system to heat mode laser exposure. Preferably, the sensitising material comprises a material which includes at least one sulphur, selenium or tellurium containing group and the sensitising layer additionally comprises a hydrophilic material. The invention provides lithographic printing plate precursors having high sensitivity which may be imagewise exposed by means of a high intensity laser beam to provide press ready plates showing high image quality, good press properties and high durability on press without the requirement for the use of intermediate film and developer chemistry.

1 . A lithographic printing plate precursor comprising: 
 (a) a grained and anodised aluminium substrate, having provided thereon    (b) a metallic layer, on top of which is applied    (c) a layer comprising at least one sensitising material which adsorbs on to the metallic surface and thereby sensitises the system to heat mode laser exposure.    
     
     
         2 . A lithographic printing plate precursor as defined in    claim 1    wherein said metallic layer comprises a silver layer.  
     
     
         3 . A lithographic printing plate precursor as defined in    claim 1    wherein said metallic layer has a thickness of from 1 nm to 100 nm.  
     
     
         4 . A lithographic printing plate precursor as defined in    claim 1    wherein said sensitising material comprises a material which includes at least one sulphur, selenium or tellurium containing group.  
     
     
         5 . A lithographic printing plate precursor as defined in    claim 4    wherein said sulphur, selenium or tellurium containing group comprises a thiol, substituted thio, disulphide, thioacid, thioamide or isothiocyanate group, or a selenium and tellurium analogue thereof.  
     
     
         6 . A lithographic printing plate precursor as defined in    claim 1    wherein said sensitising material comprises a cationic material.  
     
     
         7 . A lithographic printing plate precursor as defined in    claim 6    wherein said cationic material comprises a cationic surfactant or cationic dye.  
     
     
         8 . A lithographic printing plate precursor as defined in    claim 1    wherein said sensitising material is present in said layer to the extent of between 5 and 50%.  
     
     
         9 . A lithographic printing plate precursor as defined in    claim 1    wherein said layer containing at least one sensitising material has, in the absence of other materials, a coating thickness of between a monolayer and 0.5 μm.  
     
     
         10 . A lithographic printing plate precursor as defined in    claim 1    wherein said layer containing at least one sensitising material comprises at least one other material and has a dry coating weight of between 0.01 and 10 g/m 2 .